In automatic photographic color printing, the printing of a blank (unexposed or completely exposed) frame is a waste of time and materials. It is well known in automatic photographic printers and negative scanners to attempt to detect unexposed frames by examining the distribution of densities in parts of the film image, and to formulate some criteria for detecting unexposed frames. For example, U.S. Pat. No. 4,239,384 issued Dec. 16, 1980, to Treiber, discloses a negative scanning system that measures the average densities of different zones of a negative, defined as foreground, background and central zones, and predicts the unprintability of an image frame thereby.
Photographic printers have been proposed that scan a color image point by point to produce a digital color image. The digital color image is processed in a digital computer to improve tone-scale and color balance, and then the digital color image is printed by scanning the processed digital image onto an output medium such as color photographic paper.
In such scanning type color photographic printers, it is also desirable to automatically detect and not print blank frames in a photographic film. Although the methods of detecting blank frames employed in the prior art were appropriate for the sophistication of the equipment available at the time, in the scanning color photographic printer because of the nature of the scanning reproduction process, orders of magnitude more image density data is available for ascertaining the printability of an original. As a result, although the prior art methods of detecting blank film frames were successful and appropriate for the existing state of the art, improvements in detection accuracy can be made with the greater amounts of image data available in a scanning type photographic printer.
It is the object of the invention to provide a method for detecting blank frames of photographic originals in a scanning type photographic color printer that is capable of more accurately detecting such blank frames by making use of the greater quantity of image data available in such scanning type printers.